Chemical-mechanical planarization, or chemical-mechanical polishing (CMP), is process of smoothing surfaces with a combination of chemical and mechanical forces. Polishing rates during CMP are somewhat size dependent, with larger features being polished slower than smaller features. Accordingly, CMP of wafers with large size variation represents a conflict between over-polishing small sized features and under-polishing large sized features.
Many device fabrications patterned on wafers have large device size variations. For example, microelectromechanical systems (MEMS) devices, optical devices for energy assisted magnetic recording (EAMR), optical structures, bio-optical devices, micro-fluidic devices, and magnetic writers may have device size variations large enough to present a challenge to CMP processes. For example, EAMR devices sizes can vary between 400 nm to 75 μm. For magnetic writers, the size can vary from the pole tip below 100 nm to the yoke area of around 5 μm.